Marine Engineering

These are measures designed to remove NOx from the exhaust gas by downstream cleaning technique. The most common secondary measures are – SCR ( Selective catalytic reduction) :- In this system the exhaust gas is mixed with ammonia before passing through a layer of special catalyst at a temperature between 300 deg Celsius to 450 deg Celsius. The NOx is reduced to gaseous and harmless by-products of water and nitrogen. SNCR( Selective non-catalytic reduction) :- In case of SNCR, the reaction between ammonia and NOx takes place in a gaseous phase in a temperature window of between 800 and 900 deg Celsius. The most effective method of NOx reduction is a secondary measure.  The advantages are:- Secondary measures reduce NOx in case of SCR of up to 80- 95% and in case of SNCR 30-50%. Whereas primary measures average Nox reduction is up to 25- 35%. Possible side effects of primary measures are lower overall energy efficiency, increased carbon mono-oxide, and soot formation and hydrocarbon...